Why is the Earth self-rotating?

Question

What drives this happen? Would it be the internal energy or by an external force? I did try to Google the answer, but could not find a good one.

Answer 1

In short, it continues to rotate simply because it has no reason to stop rotating. Imagine I have a puck and I whack it across an ice-rink. The puck will continue to travel at the same speed until it hits a wall; i.e it will stay the same unless there is a reason not to. This is conservation of linear momentum as shown here.

The same thing happens with spinning objects too. Unless a spinning object has a reason to stop spinning, it will continue to spin for the rest of its life. This is known as conservation of angular momentum as shown here.

An interesting fact to note: Due to tidal acceleration, the Earth is actually slowly stopping it's rotation. This is due to, for lack of a better way of saying it, the moon giving the Earth a reason to slow down. Have no fear though, this will only continue until the rotational period of Earth matched the orbital period of the Moon, or in other words, the same side of the moon always faces the earth.